As the world's population continues its rapid growth, there is a rising issue of waste disposal. Food waste is no exception. For example, in the United States, it is estimated that food loss accounts for 133 billion pounds of waste per year and, unsurprisingly, has an incredible impact on the environment. This waste accounts for over twenty percent of total U.S. municipal solid waste discards after recycling and composting. Shockingly, wasted food accounts for the single largest component of disposed municipal solid waste.
Furthermore, food waste is a leading contributor to landfill methane emissions, which themselves constitute approximately 18 percent of total methane emissions in the United States. Indeed, landfills are the third largest methane source in the United States.
Because of the significant issues presented by disposing of food waste, the government has begun implementing programs to mitigate the effects of wasted food. At a state level, attempts are being made to address food waste disposal issues. For example, in California, where 5.6 million tons of annual food waste make up 18.1% of the state's overall waste stream, the California government passed a law requiring businesses to recycle “organic waste,” which is defined as “food waste, green waste, landscape and pruning waste, nonhazardous wood waste, and food-soiled paper waste that is mixed in with food waste.” CAL. PUB. RES. CODE § 42649.8 (2015). Since businesses will no longer be able to divert their organic waste to landfills, they are scrambling to determine how to dispose of these materials.
One solution is anaerobic digestion. Occurring naturally in oxygen-poor environments like marshes and landfills, anaerobic digestion takes place when microorganisms break down biodegradable material in the absence of oxygen. Commercially, anaerobic digestion technologies are used to break down widely available waste materials such as livestock manure, municipal wastewater solids, food waste, industrial wastewater and residuals, fats, oils, and grease. Thus, anaerobic digesters can be used to dispose of food waste and other biodegradable materials.
The by-products of anaerobic digestion include biogas, digestate, and water. Biogas, such as methane (CH4) and carbon dioxide (CO2), can be combusted to generate electricity and heat or can be processed into renewable natural gas and transportation fuels.
The anaerobic digestates that result from anaerobic digestion include solid and liquid residues with alkaline pH levels. Problematically, the anaerobic digestates often contains elements that cannot be digested by the anaerobic microorganisms on which the anaerobic digestion process depends. Depending on their source, digestates can contain pathogens, which can lead to human, animal, or plant disease. Furthermore, the digestates may be contaminated with heavy metals, inorganic compounds such as ammonia, and organic compounds. Additionally, the content of macro-elements, particularly nitrogen, phosphorous and potassium must be considered. Moreover, anaerobic digestates may have an undesirable appearance and odor.
Although anaerobic digestion is sometimes touted as a panacea to food waste disposal issues, the reality is that the anaerobic digestates themselves must be distributed. There is a need for an environmentally benign product derived from anaerobic digestates that is produced in such a way as to minimize the problems associated with anaerobic digestates.